My laboratory currently focus on two major research projects 1) to study the properties of novel adjuvants that induce the activation of mucosal DCs, and 2) to elucidate cellular and molecular mechanisms that rebalance overt inflammatory immune responses induced by pathogenic commensal bacteria within the mucosal side.
To achieve these two goals we focus on two projects:
Project #1. To establish a novel adjuvant platform using probiotic bacteria such as L. acidophilus, we have characterized a battery of L. acidophilus strains that were genetically modified to potentiate their adjuvanticity for inducing optimal mucosal DC-activation in vivo. Data show that one of these strains, 1973B, which does not express surface layer protein (Slp) A, activates DCs to produce significantly higher levels of IL-12 which in turn primes naïve T cells toward Th1 polarization. Moreover, 1973B strain compared to its wild type, show improved adjuvanticity in various vaccine combinations for numerous microbes by inducing robust protection against microbial challenge. Thus, the goal of this project is to establish an improved adjuvant platform using this strain for innovative vaccine strategies designed as a proof of concept against a wide array of pathogenic microbes. Three novel approaches are combined 1) improving adjuvant properties of L. acidophilus by modifying specific genes in these bacteria; 2) improving vaccine potency by specifically targeting antigen to DCs; and 3) expressing antigen in genetically modified L. acidophilus strain that serves not only as a potent adjuvant, but as an efficient delivery vehicle through an oral route. The advantages of mucosal adjuvant and antigen delivery through L. acidophilus vectors are numerous. These include an immunostimulatory capacity due to cell wall peptidoglycan, genomic CpG, lipotechoic acid (LTA) and etc of L. acidophilus as well as the ability to survive gastric acidity, enter the intestinal tract, and express the antigen in vivo at the targeted location or the desired receptor expressed on DCs. The predicted outcome is a highly effective adjuvant for a vaccine that can be administered safely by an oral route. Characterization of such a L. acidophilus strain will provide efficient tools to study its immunostimulatory properties. Such studies will also determine how these bacteria elicit balanced inflammatory immune responses in a mucosal microenvironment where resident mucosal DCs can be triggered to mobilize immunity against microbes.
Project # 2. The immune maintenance of intestinal homeostasis comprises the interaction of the microflora, gut epithelium and host innate immune cells. Deregulation of these immunological interactions may result in immune dysfunction that leads to the overt inflammation characterized as human inflammatory bowel diseases (IBD). Although the cellular and molecular mechanisms of IBD are not fully understood, data clearly indicate that chronic intestinal inflammation, induced by inflammatory cytokines (e.g., IL-12) plays a critical role. These cytokines clearly initiate the differentiation of pathogenic CD4+ Th1 cells that are strongly involved in IBD progression. Promising studies show that inhibition of the Th1-pathway mitigates disease. Additionally, like IL-12, secreted IL-23 from activated DCs that utilizes the IL-12p40 subunit is also implicated in the development of various autoimmune diseases including IBD. The inflammatory IL-23 nature has been attributed to its ability to induce IL-17 producing cells; Th17. This cytokine also activates the production of TNFα and IL-6 in DCs. Collectively, studies show that blocking the IL-12p40 signaling significantly reduced inflammation suggesting that both IL-12 and IL-23 function plays a key role in IBD. In contrast, IL-10 exerts regulatory effects on the inflammatory signals highlighting its potential ability in controlling Th1 and Th17 responses in IBD. To elucidate the role of L. acidophilus lipotechoic acid (LTA), a molecule that signals through toll like receptor 2 (TLR2) expressed on DCs, in inducing inflammatory cytokines, we disrupted the phosphoglycerol transferase gene that synthesizes LTA in these bacteria. Our data show that such gene disruption augmented IL-10 but down-regulated IL-12 levels in DCs co-cultured with L. acidophilus LTA-/-. Furthermore, L. acidophilus LTA-/- treated-DCs induced the regulation of T cell differentiation suggesting immune modulatory effects of this strain deficient for LTA on DCs. In the absence of this molecule, Lactobacillus peptidoglycan may activate the cytoplasmic Nod1/Nod2 pathways that results in the blockage of TLR2 induced NF-κB signals leading to the down-regulation of inflammatory cytokines (e.g. TNFα) in these cells. Our research efforts are currently focused on the mechanisms that elicit colitis and how such a L. acidophilus strain defective in LTA synthesis can modify potential factors in the mucosa to mitigate overt inflammatory immunity. We therefore propose to determine the regulatory mechanisms induced by L. acidophilus LTA-/- in intestinal DCs and their subsequent effects on T cell subsets, 2) to elucidate the effects of L. acidophilus LTA-/- in mouse Citrobacter rodentium infection and how microbial induced inflammation can be rebalanced to harmonize humoral and T cell mediated immunity during the bacterial clearance, and 3) to determine the effects of this LTA deficient strain on DC subsets which play a key role in non-human primates induced IBD.
Selected Publications:
Steele KE, Anderson AO, Mohamadzadeh M. 2009 Fibroblastic reticular cells and their role in viral hemorrhagic fevers. Expert Rev Anti Infect Ther. 7(4):423-35. Review.
Mohamadzadeh M. 2009 Potential factors induced by filoviruses that lead to immune supression. Curr Mol Med. Mar;9(2):174-85. Review.
Tournier JN, Ulrich RG, Quesnel-Hellmann A, Mohamadzadeh M, Stiles BG. 2009 Anthrax, toxins and vaccines: a 125-year journey targeting Bacillus anthracis. Expert Rev Anti Infect Ther. 7(2):219-36. Review.
Mohamadzadeh M, Duong T, Sandwick SJ, Hoover T, Klaenhammer TR. 2009 Dendritic cell targeting of Bacillus anthracis protective antigen expressed by Lactobacillus acidophilus protects mice from lethal challenge. Proc Natl Acad Sci U S A. 106(11):4331-6. Epub 2009 Feb 25.
Mohamadzadeh M, Klaenhammer TR. 2008 Specific Lactobacillus species differentially activate Toll-like receptors and downstream signals in dendritic cells. Expert Rev Vaccines. 2008 7(8):1155-64.
Tournier JN, Mohamadzadeh M. 2008 Microenvironmental impact on lung cell homeostasis and immunity during infection. Expert Rev Vaccines. 7(4):457-66. Review.
Mohamadzadeh M, Duong T, Hoover T, Klaenhammer TR. 2008 Targeting mucosal dendritic cells with microbial antigens from probiotic lactic acid bacteria. Expert Rev Vaccines. 7(2):163-74. Review.
